Basket catheter with multiple location sensors

ABSTRACT

An improved basket catheter is provided that is particularly useful for mapping the heart. The catheter comprises an elongated catheter body having proximal and distal ends and at least one lumen therethrough. A basket-shaped electrode assembly is mounted at the distal end of the catheter body. The basket assembly has proximal and distal ends and comprises a plurality of spines connected at their proximal and distal ends. Each spine comprises at least one electrode. The basket assembly has an expanded arrangement wherein the spines bow radially outwardly and a collapsed arrangement wherein the spines are arranged generally along the axis of the catheter body. The catheter further comprises a distal location sensor mounted at or near the distal end of the basket-shaped electrode assembly and a proximal location sensor mounted at or near the proximal end of the basket-shaped electrode assembly. In use, the coordinates of the distal location sensor relative to those of the proximal sensor can be determined and taken together with known information pertaining to the curvature of the spines of the basket-shaped mapping assembly to find the positions of the at least one electrode of each spine.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.10/839,036, filed May 5, 2004, which is a continuation of U.S.application Ser. No. 10/017,029, now U.S. Pat. No. 6,748,255 issued onJun. 8, 2004, the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The invention is directed to a catheter having a basket-shaped electrodearray with two or more location sensors to provide improved mappingcapabilities.

Electrophysiology catheters are commonly-used for mapping electricalactivity in the heart. Various electrode designs are known for differentpurposes. In particular, catheters having basket-shaped electrode arraysare known and described, for example, in U.S. Pat. No. 5,772,590, thedisclosure of which is incorporated herein by reference.

Additionally, it is generally known to incorporate into certainelectrophysiology catheters a location or position sensor fordetermining the location of electrodes being used to map electricalactivity. Such catheters are generally inserted percutaneously and fedthrough one or more major blood vessels into a chamber of the heart. Alocation sensor in the catheter, typically near the catheter's distalend, gives rise to signals that are used to determine the position ofthe device relative to a frame of reference that is fixed eitherexternally to the body or to the heart itself. The location sensor maybe active or passive and may operate by generating or receivingelectrical, magnetic or ultrasonic energy fields or other suitable formsof energy known in the art.

U.S. Pat. No. 5,391,199, the disclosure of which is incorporated hereinby reference, describes a position-responsive catheter comprising aminiature sensor coil contained in the catheter's distal end. The coilgenerates electrical signals in response to externally-applied magneticfields, which are produced by field-generator coils placed outside thepatient's body. The electrical signals are analyzed to determinethree-dimensional coordinates of the coil.

International Publication No. WO 96/05768, the disclosure of which isalso incorporated herein by reference, describes a position-responsivecatheter comprising a plurality of miniature, preferably non-concentricsensor coils fixed in its distal end. As in U.S. Pat. No. 5,391,1999,electrical signals generated by these coils in response to anexternally-applied magnetic field are analyzed so as to determine, forexample, six-dimensional position and orientation coordinates of thesecoils.

Multiple position-sensing devices may be placed in a known,mutually-fixed spatial relation at or adjacent to the distal end of acatheter, as described, for example, in International Publication No. WO97/24983, the disclosure of which is incorporated herein by reference.This publication describes a catheter having a substantially rigidstructure at its distal end, to which one or more position sensors arefixed. The sensors are used to determine the position and orientation ofthe rigid structure.

SUMMARY OF THE INVENTION

The present invention is directed to an improved catheter having abasket-shaped electrode assembly. The basket-shaped electrode assemblycan expand into a variety of positions and has two or more locationsensors for determining the location of electrodes mounted on theassembly.

In one embodiment, the invention is directed to a catheter comprising anelongated catheter body having proximal and distal ends and at least onelumen therethrough. A basket-shaped electrode assembly is mounted at thedistal end of the catheter body. The basket assembly has proximal anddistal ends and comprises a plurality of spines connected, directly orindirectly, at their proximal and distal ends. Each spine comprises atleast one electrode. The basket assembly has an expanded arrangementwherein the spines bow radially outwardly and a collapsed arrangementwherein the spines are arranged generally along the axis of the catheterbody. The catheter further comprises a distal location sensor mounted ator near the distal end of the basket-shaped electrode assembly and aproximal location sensor mounted at or near the proximal end of thebasket-shaped electrode assembly. In use, the coordinates of the distallocation sensor relative to those of the proximal sensor can bedetermined and taken together with known information pertaining to thecurvature of the spines of the basket-shaped mapping assembly to findthe positions of the at least one electrode of each spine.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a catheter according to the invention.

FIG. 2 is a close-up perspective view of the basket-shaped electrodeassembly, the housing, and the distal end of the catheter body of thecatheter shown in FIG. 1.

FIG. 3 is an end cross-sectional view of the distal end of the electrodeassembly shown in FIG. 2.

FIG. 4 is an end cross-sectional view of the housing and the distal endof the catheter body shown in FIG. 2.

FIG. 5 is a side cross-sectional view of the housing and the distal endof the catheter body of the catheter shown in FIGS. 1 to 4.

FIG. 6 is a side cross-sectional view of the control handle and theproximal end of the catheter body of the catheter shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

The invention is directed to a catheter having a basket-shaped electrodearray with two or more location sensors mounted at its distal end. Asshown in FIG. 1, the catheter comprises an elongated catheter body 12having proximal and distal ends, a control handle 16 at the proximal endof the catheter body, and a basket-shaped electrode assembly 18 mountedat the distal end of the catheter body 12.

The catheter body 12 comprises an elongated tubular construction havinga single, axial or central lumen (not shown), but can optionally havemultiple lumens if desired. The catheter body 12 is flexible, i.e.,bendable, but substantially non-compressible along its length. Thecatheter body 12 can be of any suitable construction and made of anysuitable material. A presently preferred construction comprises an outerwall made of polyurethane or PEBAX.RTM. (polyether block amide). Theouter wall comprises an imbedded braided mesh of stainless steel or thelike to increase torsional stiffness of the catheter body 12 so that,when the control handle 16 is rotated, the distal end of the catheterbody will rotate in a corresponding manner.

The outer diameter of the catheter body 12 is not critical, but ispreferably no more than about 8 french, more preferably 7 french.Likewise the thickness of the outer wall is not critical, but ispreferably thin enough so that the central lumen can accommodate apuller wire, lead wires, sensor cables and any other wires, cables ortubes. If desired, the inner surface of the outer wall is lined with astiffening tube (not shown) to provide improved torsional stability. Anexample of a catheter body construction suitable for use in connectionwith the present invention is described and depicted in U.S. Pat. No.6,064,905, the entire disclosure of which is incorporated herein byreference.

The basket-shaped electrode assembly 18 is mounted to the distal end ofthe catheter body 12. As shown in FIG. 2, the basket-shaped electrodeassembly 18 comprises five spines 20 or arms mounted, preferablygenerally evenly-spaced, around an expander 22 so that the expanderforms the axis of the electrode assembly. The spines 20 are allattached, directly or indirectly, to the expander 22 at their distalends, and to the catheter body 12 at their proximal ends. As describedin more detail below, the expander is moved longitudinally to expand andcontract the electrode assembly, so that, in the expanded position thespines 20 are bowed outwardly and in the contracted position the spinesare generally straight. As will be recognized by one skilled in the art,the number of spines 20 can vary as desired depending on the particularapplication, so that the assembly has at least two spines, preferably atleast three spines, and as many as eight or more spines. As used herein,the term “basket-shaped” in describing the electrode assembly 18 is notlimited to the depicted configuration, but can include other designs,such as spherical or egg-shaped designs, that include a plurality ofexpandable arms connected, directly or indirectly, at their proximal anddistal ends.

Each spine 20 comprises a flexible wire 24 with a non-conductivecovering 26 on which one or more ring electrodes 28 are mounted. In apreferred embodiment, the flexible wires 24 each comprise a flat Nitinolwire and the non-conductive coverings 26 each comprise a biocompatibleplastic tubing, such as polyurethane or polyimide tubing. Alternatively,the spines 20 can be designed without the internal flexible wire 24 if asufficiently rigid nonconductive material is used for the non-conductivecovering 26 to permit expansion of the electrode assembly 18, so long asthe spine has an outer surface that is non-conductive over at least apart of its surface for mounting of the ring electrodes 28.

Each of the ring electrodes 28 on the spines 20 is electricallyconnected to an appropriate mapping or monitoring system and/or sourceof ablation energy by means of an electrode lead wire 29. Each electrodelead wire 29 extends through the control handle 16, through a lumen inthe catheter body, and into the non-conductive covering 26 of thecorresponding spine 20. Each lead wire 29 is attached to itscorresponding ring electrode 28 by any suitable method.

A preferred method for attaching a lead wire 29 to a ring electrode 28involves first making a small hole through the wall of thenon-conductive covering 26. Such a hole can be created, for example, byinserting a needle through the non-conductive covering 26 and heatingthe needle sufficiently to form a permanent hole. The lead wire 29 isthen drawn through the hole by using a microhook or the like. The end ofthe lead wire 29 is then stripped of any coating and welded to theunderside of the ring electrode 28, which is then slid into positionover the hole and fixed in place with polyurethane glue or the like.Alternatively, each ring electrode 28 is formed by wrapping a lead wire29 around the non-conductive covering 26 a number of times and strippingthe lead wire of its own insulated coating on its outwardly facingsurfaces.

As shown in the depicted embodiment, the expander 22 is generallycoaxial with the catheter body 12. The expander 22 has a distal end atthe distal end of the electrode assembly 18 and a proximal end extendingout the distal end of the catheter body 12 and attached to the controlhandle 16, as will be described further below, so that the expander canbe moved longitudinally relative to the catheter body 12 to therebyexpand and contract the electrode assembly. The expander 22 comprises amaterial sufficiently rigid to achieve this function. In a preferredembodiment, the expander 22 comprises braided polyimide tubing, i.e.,tubing having inner and outer layers of polyimide with a braidedstainless steel mesh therebetween, as is generally known in the art. Theexpander has a guidewire lumen 30 that extends along its entire length.As will be described further below, the guidewire lumen 30 permits aguidewire to extend through the entire length of the catheter forintroduction of the catheter into the body.

Alternatively, manipulation of the electrode assembly 18 can be achievedusing a puller wire (not shown) that extends through the catheter body12 and is fixed at its distal end to the distal end of the mappingassembly and at its proximal end to the control handle 16. Such a pullerwire arrangement is disclosed, for example, in U.S. Pat. No. 5,772,590,the disclosure of which is incorporated herein by reference. Any othermeans for expanding and contracting the electrode assembly 18 can alsobe used in accordance with the invention. Alternatively, thebasket-shaped mapping assembly 18 may be expanded and contracted bymoving a guiding sheath proximally off the basket and distally over thebasket, respectively, so that the catheter itself does not need toinclude a means for expanding and contracting the basket.

The catheter further includes two location sensors 32 and 34 forproviding location information about each of the ring electrodes on theelectrode assembly 18. The distal location sensor 32 is mounted at ornear the distal end of the electrode assembly 18, and the proximallocation sensor 34 is mounted at or near the proximal end of theelectrode assembly, either on the assembly or on the catheter body, asdescribed further below.

Each location sensor 32 and 34 is connected to a corresponding sensorcable 36 that extends through the catheter body 12 and control handle 16and out the proximal end of the control handle within an umbilical cord(not shown) to a sensor control module (not shown) that houses a circuitboard (not shown). Alternatively, the circuit board can be housed withinthe control handle 16, for example, as described in U.S. Pat. No.6,024,739, the disclosure of which is incorporated herein by reference.The sensor cable 36 comprises multiple wires encased within a plasticcovered sheath. In the sensor control module, the wires of the sensorcable are connected to the circuit board. The circuit board amplifiesthe signal received from the corresponding location sensor and transmitsit to a computer in a form understandable by the computer by means ofthe sensor connector at the proximal end of the sensor control module.Also, because the catheter is designed for single use only, the circuitboard preferably contains an EPROM chip that shuts down the circuitboard approximately twenty-four hours after the catheter has been used.This prevents the catheter, or at least the location sensor, from beingused twice.

Preferably each location sensor 32 and 34 comprises amagnetic-field-responsive coil, as described in U.S. Pat. No. 5,391,199,or more preferably, a plurality of such coils, as described inInternational Publication WO 96/05758. The plurality of coils enablessix-dimensional position and orientation coordinates to be determined.Alternatively, any suitable position sensor known in the art may beused, such as electrical, magnetic or acoustic sensors. Suitablelocation sensors for use with the present invention are also described,for example, in U.S. Pat. Nos. 5,558,091, 5,443,489, 5,480,422,5,546,951, and 5,568,809, and International Publication Nos. WO95/02995, WO 97/24983, and WO 98/29033, the disclosures of which areincorporated herein by reference. A preferred electromagnetic mappingsensor has a length of from about 3 mm to about 7 mm, preferably about 4mm.

Alternatively, one of the location sensors 32 and 34 can comprise a bendsensor, which generates signals responsive to a bend radius of thespines 20. Such a bend sensor can comprise one or more piezoelectricsensors, as are known in the art, which generate electrical signalsproportional to a force or torque exerted thereon when the catheterbends. Alternatively, a bend sensor can comprise one or more strainsensors, as are known in the art, or a fiberoptic sensor, wherein thebend radius is determined by measuring the loss and/or back-reflectionof light in an optical fiber, as is also known in the art.

The coordinates of the distal sensor 32, relative to those of theproximal sensor 34, are determined and taken together with other knowninformation pertaining to the curvature of the spines 20 of thebasket-shaped mapping assembly 18. This information is used to find thepositions of the ring electrodes 28 mounted on the spines 20.

A preferred construction of the distal end of the electrode assembly 18is depicted in FIG. 3. The distal end of the expander 22 and the distallocation sensor 32 are held together with a first short piece ofplastic, preferably polyimide, tubing 38. The distal ends of theflexible Nitinol wires 24 that form the spines 20 are mounted,preferably evenly-spaced, around the first piece of tubing 38. Theflexible wires 24 are held in place by a second short piece of plastic,preferably polyimide, tubing 40. A generally-rigid ring 42 is thenmounted around the construction over the second short piece of tubing 40to maintain a generally round shape. The generally-rigid ring 42 can bemade of metal or plastic, so long as it is sufficient rigid to achievethe above-stated function. An outer tubing 44, preferably made ofpolyurethane or polyimide, then covers the entire construction over thegenerally-rigid ring 42 so that the distal end of the electrode assembly18 is generally atraumatic. If desired, the construction can be heldtogether by polyurethane glue or the like. The outer tubing 44 andgenerally-rigid ring 42 are slightly longer than the first and secondplastic tubings 38 and 40, so that the proximal ends of the outer tubingand generally-rigid ring extend beyond the proximal ends of the firstand second plastic tubings. The non-conductive coverings 26 extend intothe outer tubing 44 and generally-rigid ring 42, but end before thefirst and second plastic tubings so that only the flexible wires 24 aremounted between the first and second plastic tubings. The sensor cable36 attached to the distal location sensor 32 extends through one of thenon-conductive coverings 26 and into the distal end of the catheter body12, as described further below. As would be recognized by one skilled inthe art, other arrangements for attaching the expander 22 to the distalends of the flexible Nitinol wires 24 and for mounting the distallocation sensor 32 near the distal end of the electrode assembly 18could also be used in accordance with the invention.

A preferred construction of the proximal end of the electrode assembly18 and distal end of the catheter body 12 is shown in FIGS. 4 and 5. InFIG. 5, only one spine 20 of the electrode assembly 18 is shown forclarity. A short plastic housing 43, preferably made of PEEK (polyetheretherketone), joins the distal end of the catheter body 12 and proximalend of the electrode assembly 18 and houses the proximal location sensor34. Preferably the plastic housing 43 has a length of about 11 mm. Ifthe plastic housing 43 is too long, it can disadvantageously affect theflexibility of the distal end of the catheter body. The proximal end ofthe plastic housing 43 is mounted on the distal end of the catheter body12 by any suitable method, preferably with polyurethane glue or thelike.

The expander 22 must be afforded longitudinal movement within thecatheter body 22. Accordingly, a tunnel 44 is formed from a piece ofpolyimide tubing or the like and is provided near the distal end of thecatheter body 12 through which the expander 22 extends. The flexibleNitinol wires 24 are mounted, preferably evenly-spaced, between aproximal tubing 46 and an outer proximal ring 48, both of which arepreferably made of polyimide, and held in place with polyurethane glueor the like. The proximal tubing 46 and outer proximal ring 48 arepreferably relatively short, e.g., about 3 mm in length. Preferably theelectrode lead wires 29 and sensor cable 36 that is attached to thedistal location sensor 32 are also afforded some longitudinal movementwithin the catheter body 12 so that they do not break when the catheterbody bends. Accordingly, in the depicted embodiment, the lead wires 29and sensor cable 36 that is attached to the distal location sensor 32extend within the proximal tubing 46 though which the expander 22 andtunnel 44 also extend, so that these components are not fixed in placealong with the flexible Nitinol wires 24. This entire construction ismounted in the plastic housing 43. The proximal ends of thenon-conductive coverings 26 of the spines 20 also extend into theplastic housing 43, but preferably end prior to the distal ends of theproximal tubing 46 and outer proximal ring 48.

The proximal location sensor 34 is also mounted within the housing 43.In the depicted embodiment, a second tunnel 50 is provided at thejunction of the catheter body 12 and housing 43, with its proximal endextending into the catheter body and its distal end extending into thehousing. The tunnel 50 is preferably made of polyimide and has a lengthranging from about 5 to 7 mm. The tunnel 50 protects the expander 22,electrode lead wires 29 and sensor cable 36 that is attached to thedistal location sensor 32 from being glued to the catheter at thejunction of the catheter body and housing during assembly. Prior toassembly, the proximal location sensor 34 is mounted in a window 52 ofthe second tunnel 50. The proximal location sensor preferably has alength of about 1 to 3 mm. The sensor cable 36 attached to the proximallocation sensor 34 extends through the second tunnel 50 and catheterbody 12 along with the other components. Accordingly, all of thesecomponents are afforded longitudinal movement at the junction of thecatheter body 12 and housing 43.

Longitudinal movement of the expander 22 relative to the catheter body12, which results in expansion of the electrode assembly 18, isaccomplished by manipulation of the control handle 16. As shown in FIG.6, the control handle 16 comprises a generally-hollow handle housing 54and a piston 56 slidably mounted within the distal end of the handlehousing. The proximal end of the catheter body 12 is fixedly attached tothe distal end of the piston 56 by a shrink sleeve (not shown), as isgenerally known in the art, or by any other suitable method.

Within the control handle 16, the proximal end of the expander 22extends through a passage 57 in the piston 56, through the handlehousing 54 and into a support tube 58, preferably made of braidedpolyimide or PEBAX.RTM. The support tube 58 extends out the proximal endof the control handle 16 and terminates in a luer hub 60. The supporttube 58 and expander 22 are together fixedly attached to the handlehousing 54 by any suitable method, preferably with polyurethane glue orthe like. The guidewire lumen 30 of the expander 22 can also be used forinfusion of fluids through the catheter, as is generally known in theart.

In a preferred embodiment, the piston 56 is approximately about 2 incheslong, and the support tube 58 and expander 22 are attached to the handlehousing 54 at a position about 0.5 inch distal to the proximal end ofthe handle and about 1 inch proximal to the proximal end of the pistonin the neutral position. The piston is in the neutral position when theelectrode assembly 18 is generally flat, i.e., not expanded.

The lead wires 29 and sensor cables 36 also extend through the pistonpassage 57 and handle housing 54 and are attached to a suitableconnector 62 at the proximal end of the handle housing. Alternatively,the lead wires 29 and sensor cables 36 can extend through protectivesupport tubes (not shown), similar to the support tube 58 that carriesthe expander 22, which have distal ends inside the handle housing 54 andproximal ends attached to appropriate connectors.

To use the catheter of the invention, an electrophysiologist introducesa guiding sheath, guidewire and dilator into the patient, as isgenerally known in the art. A suitable guiding sheath for use inconnection with the inventive catheter is the PREFACE™. Braided GuidingSheath (commercially available from Biosense Webster, Inc., Diamond Bar,Calif.). The dilator is removed, and the catheter is introduced throughthe guiding sheath whereby the guidewire lumen in the expander 22permits the catheter to pass over the guidewire. The guiding sheathcovers the spines 20 of the electrode assembly 18 internally in acollapsed position so that the entire catheter can be passed down a veinor artery to a desired location. Once the distal end of the catheterreaches the desired location, the guiding sheath is withdrawn. Theexpander 22 is then manipulated so that the spines 20 of the electrodeassembly 18 flex outwardly into an expanded arrangement. In such anarrangement the spines 20 and the ring electrodes 28 contact the tissueof the heart. As will be recognized by one skilled in the art, theelectrode assembly 18 can be fully or partially expanded in a variety ofconfigurations depending on the configuration of the region of the heartbeing mapped.

Using the ring electrodes 28 on the spines 20 of the electrode assembly18 in combination with the distal end proximal location sensors 32 and34, the electrophysiologist can map local activation time, which canguide the electrophysiologist in providing therapy to the patient. Thecatheter can include one or more reference ring electrodes mounted onthe catheter body 12, or one or more reference electrodes can be placedoutside the body of the patient. By using the inventive catheter withthe multiple electrodes 28 on the basket-shaped electrode assembly 18,the electrophysiologist can obtain a true anatomy of the heart bymeasuring less points than with traditional catheters, allowing him tomap the heart more quickly. Moreover, by introducing the electrodeassembly 18 over the guidewire, the electrophysiologist can remove thecatheter from the heart and later reintroduce the electrode assembly tothe same position after therapy, thereby permitting theelectrophysiologist to accurately view the results of the therapy. Priorbasket catheter designs did not permit this reproducibility.

If desired, the catheter can include a steering mechanism for deflectionof the distal end of the catheter body 12. With such a design, thedistal end of the catheter body 12 preferably comprises a short lengthof tubing, e.g., 2 to 4 inches, that is more flexible that the remainderof the catheter body. A suitable steering mechanism comprises a pullerwire (not shown) that extends from a proximal end in the handle throughthe catheter body and into an off axis lumen in the catheter tipsection. Within the catheter body, the puller wire extends through aclosely wound coil that is bendable but substantially compressible. Thecoil is fixed near the proximal and distal ends of the catheter body andprevents deflection of the catheter body. The distal end of the pullerwire is anchored at the distal end of the catheter body proximal to theproximal end of the basket. The proximal end of the puller wire isanchored to a movable member in the handle that can be moved relative tothe catheter body. Proximal movement of the movable member relative tothe catheter body results in deflection of the catheter tip section. Anexample of such a steering mechanism and construction is described inmore detail in U.S. Pat. No. 6,064,905, the disclosure of which isincorporated herein by reference.

If a steering mechanism is included, the control handle 16 may be of anysuitable construction for manipulating two wires, in this case, theexpander 22 and a puller wire. Preferably the handle has a pair ofmovable members to which the expander and puller wire attach, such ashandles typically used for bidirectional and multidirectional catheters.Examples of such handles are disclosed in U.S. Pat. Nos. 6,210,407,6,198,974, 6,183,463, 6,183,435, 6,171,277, and 6,123,699, thedisclosures of which are incorporated herein by reference.

In an alterative embodiment (not shown), the spines 20 do not includenon-conductive coverings 26 so that the flexible Nitinol wires 24 eachact as an elongated electrode. In such an embodiment, the sensor cable36 attached to the distal location sensor 32 can extend through a secondlumen (not shown) in the expander 22. Electrode lead wires 29 can thenbe attached to the proximal ends of the spines 20 within the catheterbody 12. As would be recognized by one skilled in the art, otherelectrode configurations on the spines 20 could also be used inaccordance with the invention.

In another alternative embodiment (not shown), the catheter does notinclude a control handle. In such an embodiment, the proximal end of theexpander 22 will extend out the proximal end of the catheter body 12 andcan be manipulated directly. However, such a design is less desirablefrom a practical standpoint, as it may be more difficult for theelectrophysiologist to control.

The preceding description has been presented with references topresently preferred embodiments of the invention. Persons skilled in theart and technology to which this invention pertains will appreciate thatalterations and changes in the described structures can be practicedwithout meaningfully departing from the principle, spirit and scope ofthis invention. Accordingly, the foregoing description should not beread as pertaining only to the precise structures described and shown inthe accompanying drawings, but rather should be read as consistent withand as support for the following claims, which are to have their fullestand fairest scope

1. A catheter comprising: an elongated catheter body having proximal anddistal ends and at least one lumen therethrough; an electrode assemblyat the distal end of the catheter body, the electrode assembly havingproximal and distal ends and comprising a plurality of spines, thespines comprising a plurality of electrodes; an expander having proximaland distal ends, the expander forming a longitudinal axis of theassembly, the spines attached at their proximal and distal ends to theexpander, wherein the electrode assembly has an expanded arrangementwhen the expander is moved proximally along the longitudinal axisrelative to the catheter body and the electrode assembly has a collapsedarrangement when the expander is moved distally along the longitudinalaxis relative to the catheter body; a distal electrode location sensormounted at or near the position where the distal ends of the spines areconnected; a proximal electrode location sensor mounted at or near theproximal end of the assembly, whereby, in use, the coordinates of thedistal electrode location sensor relative to those of the proximalelectrode location sensor can be determined and taken together withknown information pertaining to the curvature of the spines of theassembly to find the positions of each of the plurality of electrodes onthe spines; and a control handle for manipulating the expander.
 2. Thecatheter of claim 1, wherein the control handle comprises: a generallyhollow handle housing having proximal and distal ends; and a pistonslidably mounted within the distal end of the handle housing.
 3. Thecatheter of claim 2, wherein the proximal end of the catheter body isfixedly attached to the distal end of the piston.
 4. The catheter ofclaim 1, wherein the assembly is basket-shaped.
 5. The catheter of claim1, wherein the assembly is egg-shaped.
 6. The catheter of claim 1,wherein the assembly is spherical.
 7. The catheter of claim 1, whereinthe spines bow radially outwardly when the assembly is in the expandedarrangement.
 8. The catheter of claim 1, wherein each spine has anon-conductive outer surface on which one or more ring electrodes aremounted.
 9. The catheter of claim 1, wherein each spine comprises aninternal flexible wire and a non-conductive covering over the flexiblewire on which one or more ring electrodes are mounted.
 10. The catheterof claim 1, wherein the basket-shaped electrode assembly has at leastthree spines.
 11. The catheter of claim 1, wherein the basket-shapedelectrode assembly has at least five spines.
 12. The catheter of claim1, wherein the proximal electrode location sensor is mounted in thedistal end of the catheter body.
 13. The catheter of claim 1, whereinthe proximal and distal electrode location sensors each comprise anelectromagnetic location sensor.
 14. The catheter of claim 9, whereinthe internal flexible wire of each spine comprises nitinol.
 15. Thecatheter of claim 1, wherein the proximal end of the expander isattached to the control handle.
 16. The catheter of claim 1, wherein theexpander comprises a puller wire.
 17. The catheter of claim 1, whereinthe expander has a lumen extending therethrough.
 18. The catheter ofclaim 1, wherein the expander comprises plastic tubing.
 19. The catheterof claim 1, wherein the expander comprises braided plastic tubing. 20.The catheter of claim 1, wherein the expander comprises braidedpolyimide tubing.
 21. The catheter of claim 1, further comprising atleast one ring electrode on each spine.
 22. The catheter of claim 1,wherein each of the distal and proximal location sensors comprises atleast one magnetic-field-responsive coil.
 23. The catheter of claim 22,wherein each of the proximal and distal location sensors comprises sixmagnetic-field-responsive coils.
 24. The catheter of claim 1, whereineach of the distal and proximal location sensors comprises a bendsensor, wherein the bend sensor is adapted to generate signalsresponsive to a bend radius of the spines.
 25. The catheter of claim 24,wherein each bend sensor comprises a piezoelectric sensor, wherein thepiezoelectric sensor is adapted to generate electrical signalsproportional to a force or torque exerted on the sensor when thecatheter bends.